1. Field of the Invention
The present invention relates to a data erasing device and, more particularly, to a data erasing device for a hard disk device used as a storage device in a computer.
2. Description of the Related Art
Conventionally, in computers such as personal computers and the like, recording media for recording programs and data are necessary and, in recent years, hard disk devices using a disk coated with a magnetic material have become popular as such recording media. Such hard disk devices are built into the computer or are used as external hard disk devices connected to the computer via a cable, data being written into at least one internal disk via at least one head. The storage capacity of these types of hard disks has been steadily increasing over the years.
Meanwhile, personal computers are being sold in new formats year by year along with advances in the operating systems that drive them, the processing speed of CPUs (central processing units), the expansion of communication functions, the increase in the capacity of hard disk devices, and the like, so that there is a tendency for old personal computers to be replaced with new personal computers within a short period of time.
Hard disk devices built into old computers that have been disposed of when replaced by new computers, and hard disk devices with small memory capacities which have been disposed of when replaced by new hard disk devices with larger memory capacities, still contain large amounts of various types of data which were written into the hard disk device while it was in use. Amongst this data is data, such as personal information, internal company information and the like, that must not be leaked to a third person. In such cases it is common to perform an erasing process using computer software to erase data from the hard disk device prior to disposal.
However, this data erasing process is simply a process which allows data to be written over regions of the disks in the hard disk device in which data has been previously stored. Consequently, all of the data which had been stored on the disk is not completely erased. Thus, regarding hard disk devices from which data has not been completely erased in this manner, a malicious third person, using special software, can read the remaining data.
In this regard, as methods for completely erasing data recorded on a hard disk device, a method of writing random data on the entire surface of the magnetic disk in the hard disk devices and a method of forcefully erasing data by passing the magnetic disks of hard disk device through a powerful magnetic field such as that generated by a permanent magnet or the like, are known. With respect to the first method, the existence of software for service organizations and retailers to perform this method is well known. Also, with respect to the second method, data erasing devices for erasing data by applying a strong magnetic field to magnetic disks by controlling the strength of the magnetic field applied to the spindle motor of the hard disk device are known (for example, refer to U.S. Pat. No. 6,594,099 (JP-A-2001-331904)). Because the data erasing device disclosed in U.S. Pat. No. 6,594,099 has an object of allowing reuse of the magnetic disks, data on the magnetic disk is deleted by passing one end of the magnetic disk device through a magnetic field sandwiched by permanent magnets in a state that the magnetic disk is rotated by the spindle motor.
The method of writing random data on the entire surface of the magnetic disks of the hard disk device as described above has a problem in that writing the data takes time due to the large capacity of the hard disk device, and has an additional problem in that the disposal cost increases when a service organization is asked to erase the data. On the other hand, in the data erasing device disclosed in U.S. Pat. No. 6,594,099 for erasing data by means of magnetic saturation, by passing the magnetic disk through a strong magnetic field, equipment for rotating the spindle motor is necessary, leading to the problem of an increase in the device size. Also, there is a problem in that if, for some reason, the spindle motor does not rotate, the data will not be completely erased. As explained above, the conventional data erasing device does not take into account the erasing of data with the object of only preventing data leakage from the disposed hard disk device without reusing the magnetic disk.
In order to prevent leakage of data recorded on a magnetic disk device or other magnetic recording medium such as a hard disk device to be destroyed, the inventors of the present invention have proposed a simple data erasing device capable of securely erasing data from a hard disk device in a simple operation, by placing the hard disk device on a tray and inserting and ejecting this disk device to and from the data erasing device, as shown in a second embodiment of US-2004-51989-A1(JP-A-2004-110908).
However, according to the data erasing device which the inventors of the present invention proposed in the second embodiment of US-2004-51989-A1, an erasing magnetic field is applied to the hard disk device from only one direction, thereby erasing the data recorded on the magnetic recording medium. Therefore, a large magnet must be used for the magnetic circuit that generates the erasing magnetic field. Consequently, the data erasing device becomes large and has increased weight. Further, a magnetic shielding mechanism that prevents leakage of magnetism to the outside becomes large. This results in high cost of the data erasing device.
A large magnet is used in the data erasing device for the following reason. When an erasing magnetic field is applied to the hard disk device from only one direction, data in a direction parallel with a direction of an external magnetic field can be demagnetized easily. However, data in a direction at a right angles to the direction of the external magnetic field cannot be easily demagnetized. Therefore, in order to completely erase the data, it has been necessary to use a magnet that generates a magnetic field having coercive force about two times that of the magnetic recording medium.